You don't have to do them in order, but it makes things a lot easier.
The base pack is a self-contained exe file, so you can just run that and let it do the thing.
For the i24 pack, you just need to extract the data folder to your CoH install, it has all the directory structure in place.
For the i25 pack, you need to extract the three files to the CoH install directory under /data/texture_library/MAPS/static
In all cases, choose yes to overwrite conflicting files - this is how it updates the map images. If, for some reason, you/your computer does not know what to do with a .7z file, it is a "7zip" compressed file, and you can get said program here - https://www.7-zip.org/download.html
The base pack is a self-contained exe file, so you can just run that and let it do the thing.
For the i24 pack, you just need to extract the data folder to your CoH install, it has all the directory structure in place.
For the i25 pack, you need to extract the three files to the CoH install directory under /data/texture_library/MAPS/static
In all cases, choose yes to overwrite conflicting files - this is how it updates the map images. If, for some reason, you/your computer does not know what to do with a .7z file, it is a "7zip" compressed file, and you can get said program here - https://www.7-zip.org/download.html